Video surveillance systems often include one or more video cameras positioned throughout an area of interest, where the individual cameras are movable, i.e., to pan, tilt, and/or zoom, by one or more electric motors coupled to the camera. The motors may be connected to a monitoring station through a network for receiving movement commands and, just like any other electric motor, they are subject to signal or current overloads that can damage or destroy a particular motor, thereby potentially rendering the video camera assembly inoperable.
There are numerous existing methods and devices to protect motors and motor drive circuits from short circuits. These devices range from simple fuses or positive temperature coefficient devices (“PTCs”) to integrated circuits (“ICs”) that sense the current to the motor and intercede if a peak current threshold is detected. A more sophisticated, and thus more expensive, device includes one or more motor driver ICs that can be set below a locked rotor level of current that will only intercede and break the current to the motor if the locked rotor level current is detected over a longer period of time than would otherwise be normal for a particular motor.
In addition, some motor control ICs may have locked-rotor and short circuit protection. These typically higher-end circuits often cost much more than simple fuses, PTCs or ICs providing only short-circuit protection. Many of the lower cost motor driver ICs have a fixed current limit, which is good for protecting against short circuits, but is not very useful for protecting against a locked rotor condition. A locked rotor condition often occurs during motor start-up, but a locked rotor condition occurring over an extended period of time indicates a malfunction and would likely damage the motor. From a cost standpoint, of course, it is most desirable to use the lower cost motor driver ICs with a non-integrating type of current protection rather than the costly motor ICs having locked-rotor and short circuit protection.
In addition to preventing an over-current and/or locked rotor condition, another problem in current video surveillance systems relates to the loss of video dome communication with a processor and/or monitoring station. A typical video surveillance system has a central processor, typically implemented as a part of one or more video matrix switches. The matrix switches may have keyboard inputs to facilitate manual control of the components or cameras of the surveillance system, and to provide a means for inputting system setup parameters. The matrix switches route video from the surveillance camera of interest to an operator's display monitor. Matrix switches also can be pre-programmed to sequentially select, in a pre-determined order and dwell time for example, the video inputs from assorted cameras and feed that video stream to a time lapse VCR, digital recorder or other video recording device.
In critical installations, it is often desirable, and in some cases required by law, to have continuous recording of certain video input streams. Casino gambling tables are one example. In these situations, when video coverage is lost, the table has to be shut down. In many of these situations, the video passes to a full time recorder before passing on to a matrix switch. Such a configuration allows full time recording of a particular video stream while allowing an operator to selectively view and control individual domes or cameras. Some larger systems may also have junction box arrangements where the video is either passed straight through or is amplified and passed on through. Such junction boxes generally buffer or split and re-drive the control network to allow connection of more domes or use of longer network lines than would otherwise be possible.
Any one of these example devices and configuration described above can fail in such a way as to prevent communication to the surveillance camera, even though the camera is powered and in perfect working order. In critical systems, when there is a loss of communication to the camera, but the video from the camera is still being captured and/or recorded, it would be desirable to manually aim the dome at a particular area of interest, such as a gaming table for example. However, emergency positioning of a camera can often only be achieved by routing the control to the camera from another processor, thereby bypassing the defective system device. Another option generally includes having a portable keyboard/processor that could be carried to the camera and fed into a control port on the camera. Still, rewiring the camera communication to the keyboard/processor may require an unacceptable time period to complete and/or require skilled electricians to be called in to make the repair.
Moreover, even though communication with the camera assembly may be lost, the motors of the assembly will typically still be powered to maintain their current positions. As such, any attempt to manually reposition the camera assembly, and thus the motors, will be resisted by an increase of current to the motor to counteract the manually applied torque in an effort to maintain the camera position. As a result, even if the camera assembly is operational except for the signal communication with a monitoring station or the like, an attempt to manually reposition the camera may actually cause significantly more damage as the motors become overloaded trying to stay in place.
In view of the above, it is desirable to provide a simplified solution for over-current protection for a motor, as well as to allow for the manual positioning of a video camera assembly upon interruption or malfunction of a system component.